This invention relates to rotary drill bits and more particularly relates to a novel and improved drill bit assembly of the type having pivotal cutter blades mounted at the lower end of a conventional drill string.
There is a need for a drill bit assembly which can be mounted at the lower end of a drill string in a conventional manner and is capable of carrying out high speed earth boring operations with or without fluid assist, with or without tungsten carbide buttons, cutting teeth, cutting rollers or polycrystalline and diamond inserts. Most desirably, the drill bit assembly of the present invention incorporates a unique combination and arrangement of cutters and fluid passages along one or more pivotal blade arms of a drill bit assembly.
Representative patents are U.S. Pat. No. 2,203,998 to D. J. O""Grady, U.S. Pat. No. 2,814,463 to A. W. Kammerer, Jr., U.S. Pat. No. 3,196,961 to A. W. Kammerer, U.S. Pat. No. 3,552,509 to C. C. Brown, U.S. Pat. No. 3,554,304 to H. D. Link et al, U.S. Pat. No. 3,656,564 to C. C. Brown, U.S. Pat. No. 3,684,041 to A. W. Kammerer et al and U.S. Pat. No. 5,271,472 to R. E. Leturno.
It is an object of this invention to provide for a novel and improved drill bit for earth boring operations which is highly versatile and efficient and durable in use.
Another object of the present invention is to provide for a novel and improved drill bit assembly adapted to be mounted on a conventional drill string and which employs a combination of cutter elements and jet discharge nozzles selectively positioned along the length of one or more cutter blades to achieve a uniform cutting force along the length of each blade.
A further object of the present invention is to provide for a novel and improved drill bit assembly which employs a unique combination of cutting inserts and fluid passages to carry out downhole cutting operations and specifically wherein the cutting elements may be employed alone or in combination with fluid pressure to perform different cutting and kerfing operations.
It is a still further object of the present invention to provide for a novel and improved drill bit made up of pivotal cutter blades which employ a unique combination of cutter elements and fluid passages selectively oriented and spaced along the cutting edge of each blade to maximize cutting performance and speed.
In accordance with the present invention, a drill bit assembly is adapted to be mounted on a drill string for performing earth boring operations in a subsurface formation comprising a sub connected to a lower end of the drill string, and a plurality of elongated cutter blades are pivotally secured to a lower end of the sub, the lower end of the sub including cutting elements thereon. The blades include radially inner and outer offset portions along a surface of each blade adapted to move into engagement with the formation, each of the offset portions including cutting members thereon. Fluid delivery means communicates with a fluid circulation bore in each blade for delivery of fluid under pressure through a plurality of fluid discharge ports.
In a preferred form, the cutter elements include a plurality of rotatable cutter disks which are disposed at radially spaced intervals along the length of each cutter blade, each disk oriented for rotation about an axis on the radius of curvature of the circular path of travel traced by each respective disk; and each cutting blade has offset cutting edges defined by radially spaced smaller cutter disks and larger cutter disks, respectively. In addition, an increased number of jet discharge nozzles is provided along the outer offset edge relative to those provided along the inner offset edge as a result of the greater area traversed by the outer edge. Still further, the nozzle locations are staggered with respect to the cutting element locations so that the cutting elements break up the material between the kerf lines formed by the nozzles. For example, if the nozzles are disposed only along one of the blades 17 or 18 and the cutting elements disposed along the other of the blades, the cutting elements will break up that formation material between the kerf lines L1 and L2 formed by the nozzles on the one cutting blade. If the cutting elements are positioned on both blades, they are preferably staggered with respect to one another so as to engage different radial distances in the formation between the kerf lines L1 and L2. Correspondingly, if the nozzles are positioned along both blades, they are offset with respect to one another to form kerf lines L1 and L2 at different radial distances and thereby achieve enhanced cutting action. The number and spacing of cutting elements and nozzles along the offset edges 30 and 32 will of course vary with the hardness of material being drilled, hole size and velocity of the fluid discharge.
The preferred method of drilling into a subsurface formation in accordance with the present invention comprises the steps of discharging a high velocity stream of fluid through a plurality of nozzles in at least one of a pair of rotating drill bits or blades wherein a series of kerf lines are formed in concentric circles, placing a series of cutter elements on at least one other of the blades to break up the formation material between the kerf lines formed by the jet streams through the nozzles and orienting the elements to follow or track the kerf lines formed by the nozzles to assist in breaking up the rock or other material between the kerf lines.
There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. In this regard, the term xe2x80x9cdrill stringxe2x80x9d is employed herein to interchangeably refer to a string of drill pipe(s) or casing(s) or tubing(s). As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.